Conventionally, as a container of this type, known is one having a structure in which, when the containers are stacked, a bottom-face projection provided for the upper-layer container is fitted inside a top-face opening of the lower-layer container to prevent lateral shift. Also, on both side portions of a second sidewall of the container, side projection pieces that are overlapped with a side portion of a first sidewall from the outside are provided, and by engagement of a side engaging hole formed in the side projection piece and a side engaging projection projecting from an outer face of the side portion of the first sidewall, the first sidewall and the second sidewall adjacent to each other are joined (refer to, for example, Patent Literature 1).